In many electrically operated machines, the operating components of the machine are concealed behind a outer cover such that a user of the machine would not be exposed to any of such components. This is designed from both an expediency and safety point of view such that it protects the operating components of the machine from being tampered with by users who may not be qualified to service such components and furthermore, to protect an operator from being exposed to such components that carry live electricity. To achieve such objective, the outer cover of the machine is designed to engage interlock switches that are installed in the machine which are normally engaged (or pushed down) by the outer cover such that power supply to the machine is not interrupted. The interlock switches have been used in a variety of electrically operated machines such as an office copy machine or a large variety of semiconductor process machines.
The interlock switches are frequently constructed of two parts. First, a mechanical component that consists of a shaft mounted on a spring that can be moved up and down and secondly, an electrical switch that can be switched on or off by the shaft with a very small force, i.e., a microswitch. The microswitch can be designed as an integral part of the mechanical component or as an attachment external to the mechanical component. For instance, the mechanical component can be a cylindrical shaft positioned in a hollow housing and loaded by a spring element such that when the shaft is in an extended position and not pushed down by a machine cover, the microswitch is disengaged (or deactivated) to provide a bypass circuit which possibly includes a warning lamp to indicate that the power supply to the machine has been interrupted. After an outer cover is reinstalled on the process machine, the shaft of the mechanical part is pushed down to engage (or activate) the microswitch such that a current flows through the process machine to provide power. A process machine thus designed incorporating a plurality of interlock switches enables an operation of the machine in an intended manner.
During the normal operation of a process machine, the machine may malfunction and necessitates a repair procedure to be conducted. Similarly, routine preventive maintenance procedures may also be required on process machines, for instance, replacing heating lamps before they are burned out or other expansible parts that are subjected to deterioration with usage. In either event, a power supply to the machine can not be interrupted when the outer cover of the machine is removed so that a repairman can diagnose the cause of a problem or in the case of a preventive maintenance work, to make sure that parts replaced function properly before the machine cover is reinstalled. Presently, in order to carry out the repair/maintenance work, a jumper wire must be connected for each interlock switch in order to bypass the switch. This is not only a tedious but also an inconvenient process since the jumper wires can be accidentally disconnected or damaged when work is performed on the machine.
It is therefore an object of the present invention to provide an interlock switch that does not require the use of a jumper wire when power to a machine must be maintained such as that required by a conventional interlock switch.
It is another object of the present invention to provide an interlock switch that is equipped with a latch key and a stop ring that are adapted for engaging each other.
It is a further object of the present invention to provide an interlock switch that can be latched into a permanently engaged position by locking a latch key on the shaft of the switch against a stop ring located on the housing of the switch.
It is another further object of the present invention to provide an interlock switch that further includes an indicator lamp for providing visual indication when the switch is not engaged between the latch key and the stop ring.
It is yet another object of the present invention to provide an interlock switch that can be permanently engaged to provide power to the machine even though a machine cover is removed to facilitate a repair or maintenance work to be performed on the machine.
It is still another object of the present invention to provide an interlock switch for use in a semiconductor process machine such that the machine can be serviced even when the machine cover is removed by a service personnel.